Path: utzoo!attcan!uunet!samsung!usc!ucsd!ucbvax!hplabs!hpl-opus!hpnmdla!sheppard
From: sheppard@hpnmdla.HP.COM (Roger Sheppard)
Newsgroups: comp.dsp
Subject: Re: 1 Bit D to A Revisited
Message-ID: <7070002@hpnmdla.HP.COM>
Date: 21 Nov 89 16:45:53 GMT
References: <8911201702.AA03844@en.ecn.purdue.edu>
Organization: HP Network Measurements Div, Santa Rosa, CA
Lines: 15

Yes this sounds like delta modulation but that is not new. The only recent
anouncement that concerns a 1 bit D/A is from Phillips addressing the
problem of costly and inaccurate 16/18 + D/A's on low level signals
in CD players. They claim that by drastically oversampling at x256 they
convert the parallel words to an 11.3MHz bit stream that represents a
"pulse density modulation" that is similar to delta modulation in that
it pumps up and down a filter. The rf components can be removed by gentle
filtering because there is a wide frequency difference between the information
and the data rate. Also adverse effects on the phase of inband signals are 
minimized. Since only two states are needed to go up or down a simple 1 bit
D/A can be used and the filter designed with switched capacitor technology.
Using VLSI, two chips can do the servo control, digital detection, correction,
interpolation, oversampling, and D/A conversion for a fraction of the cost
of todays players while maintaining the same S/N and better low level
linearity.